Automotive type clutches serve to provide a mechanical driving connection between the crankshaft and the flywheel of the engine and the input shaft of the transmission. The basic clutch construction has been nearly standard for many years and includes a rigid cover bolted to the flywheel of the engine; a pressure plate urged by strong springs anchored on the cover toward the flywheel for the purpose of clamping the clutch plate tightly between the pressure plate and the flywheel. The clutch plate is splined to the input shaft of the transmission for transmitting rotary power from the engine flywheel to the transmission.
The clutch is disengaged by pulling or lifting the pressure plate away from the flywheel so as to release the clutch plate which is clamped therebetween, thereby allowing the flywheel and pressure plate to continue to revolve with the crankshaft of the engine while the clutch plate and clutch disc are allowed to stop and remain stationary without transmitting rotary power to the transmission. The pressure plate is lifted away from the flywheel by a number of release fingers which are pivoted on the cover and connected to the pressure plate for prying the pressure plate away from the flywheel against the force of the strong springs. The release fingers are operated by a release bearing, sometimes known as a throw out bearing, arranged concentrically of the input shaft to the transmission. The throw out bearing is normally spaced slightly from the release fingers, and when the clutch is to be disengaged, the throw out bearing is moved into engagement with the release fingers under the influence of the release fork or throw out lever which is pivotally mounted on the stationary transmission housing. A linkage in most clutches interconnects the release fork with the clutch lever found in the operator's compartment of the vehicle.
As the clutch disc wears, it reduces in thickness; and compensation is made for the reduced thickness by the springs continually urging the pressure plate toward the flywheel so that the clutch disc remains clamped tightly therebetween. As the clutch disc wears more and more, the pressure plate must move further toward the flywheel, and as this occurs, the release fingers are tilted slightly so as to move closer and closer to the throw out bearing in its retracted position. Eventually, as sufficient wear in the clutch disc occurs, the release fingers will continually bear against the throw out bearing which cannot move significantly away from the release fingers, and as a result, the throw out bearing continually bears against the release fingers with substantial pressure. This pressure causes an influence on the pressure plate, tending to lift the pressure plate away from the flywheel and clutch disc, and as this occurs, the clutched disc may slip between the flywheel and pressure plate instead of being clamped tightly. Such slippage of the clutch disc causes excessive and unusual wear. Also, the throw out bearing will often fail under the continual pressure by the release fingers.
Substantial efforts have been made in the past to provide for readjustment of the position of the throw out bearing as the clutch disc wears so that such slippage of the clutch disc will not occur. In most clutch linkages, between the release fork and the clutch pedal, there is a manually adjustable link which may be adjusted as to length so as to readjust the rest position of the throw out bearing and reestablish a spaced relation or clearance between the throw out bearing and the release fingers. It has been experienced in the past that the adjustments in the linkage are usually inaccessible, and are usually not known to the owners of automobiles so that such linkage adjustments are simply neglected.
Numerous attempts have been made to automatically adjust the length of the linkage between the release fork and the clutch pedal, but none of such prior automatic adjusting mechanisms have found success.
A number of attempts have been made in the prior art to mechanically adjust the length of the linkage in response to wear of the clutch plate. All of these mechanisms have been exceedingly complicated for the purpose intended and have undoubtedly produced substantial wear in themselves so as to be quite unreliable.
Other prior art devices have attempted to utilize a hydraulic master cylinder operated by the clutch pedal and then the cylinder and piston arrangement for operating the release fork of the clutch while simultaneously adjusting for the reduced thickness of the clutch disc. Such mechanisms are also unduly complicated and add considerable expense to the automotive clutch mechanism which added expense is completely unnecessary.